Stripping process for plutonium



STRIPPING PROCESS FOR PLUTONIUM Morris Kolodney, New York, N.Y.,assignor to the United States of America as represented by the UnitedStates Atomic Energy Commission No Drawing. Application March 25, 1948Serial No. 17,102

3 Claims. (Cl. 204-15) This invention is related to a method of cleaninga metal, and more particularly to a method of cleaning plutonium.

Due to the known radioactive properties of plutonium and to thepossibility that it may evolve radioactive or toxic fumes, it isdesirable to cover the plutonium with a protective coating. In the past,metals such as silver, nickel, cadmium, zinc, indium and the like havefrequently been used for such a coating. At times it is necessary toremove this protective coating either because the coating is defectiveor because it is necessary to rework the plutonium. Prior to the time ofthis invention this removal has proved to be a very expensive processbecause the methods used for removing the coating such as dissolving itin chemical compounds also removed some of the very valuable plutonium.

It is, therefore, the primary object of this invention to provide amethod for efiiciently and rapidly removing metal coatings fromplutonium.

It is a further object of this invention to provide a method forremoving metal coatings from plutonium objects while at the same timeleaving the plutonium objects intact.

It is a still further object of this invention to provide a process forremoving metal coating from plutonium metal bodies efiiciently andrapidly while at the same time rendering the surface of the plutoniummetal bodies pass1ve.

The objects of this invention are achieved by the process of removingthe protective metal coatings from plutonium by immersing the coatedplutonium object as the anode in an electrolyte in which plutonium ispassive and the coating metal is not passive, using a metal as cathodewhich does not dissolve rapidly in the electrolyte and passing anelectrical current until the coating metal is removed from the saidplutonium body.

More specifically, the plutonium body is used as the anode, and metalssuch as stainless steel are used as the cathode, in an electrolyte suchas concentrated sulfuric acid or phosphate ion solutions.

The methods of this invention can best be illustrated by the followingexamples which are given for the purpose of presenting embodimentsthereof and not for the purpose of limiting the spirit or scope of theinvention. Example I presents the presently preferred embodiment of themethod of this invention.

Example I A piece of plutonium foil 1.6 inches square and 0.1 inch thickwith a silver coating 1 mil thick on each surface is immersed in 98percent sulfuric acid which has a specific gravity of 1.84. Theplutonium is used as the anode, a stainless steel block of the same sizeis used as the cathode. The container is of Pyrex glass and is left atroom temperature. An anode current density of 0.5 ampere per square inchis applied until the coating is substantially dissolved. At this timethe current ceases to flow because the plutonium is not soluble in theelectcs PatentO 2,907,700 Patented Oct. 6, 1959- ice trolyte used. Thisrequires from 3 to 5 minutes and leaves the surface bright, lustrous butpassive.

Another embodiment of the method of this invention is illustrated inExample Ilin which the phosphate ions are supplied by'tri'sodiumphosphate.

Example II A piece of plutonium 2.0 inches square and 0.1 inch thickwith a 1 mil nickel coating on each surface is placed in an aqueoussolution containing grams of trisodium phosphate per liter of water. Thevessel is Pyrex glass and the bath is maintained at room temperature.The plutonium block is used as the anode, and a similar size stainlesssteel block is used as the cathode. An anode current density of 0.4amperes per square inch is applied. After about 5 minutes the coating isremoved, the surface of the pure plutonium is rendered passive and thecurrent ceases to flow.

The method can, of course, be varied in many ways. For example, thecontainer may be any material such as Pyrex glass or stainless steelwhich is not appreciably dissolved in the electrolyte. The cathode,likewise, may be any metal such as the stainless steel used in the aboveexample, which does not appreciably dissolve in the electrolyte. Thecurrent density may be varied depending 'on the depth and nature of thecoating. As an example,

the current density may be varied from 0.1 to 1 ampere per square inchin order to quickly and efiiciently re move a 1 to 5 mil silver depositfrom the plutonium.

The method of the invention can be applied to removing types of metalother than silver or nickel. For example, the process can be applied tothe removal of metal coatings such as cadmium, zinc, indium, and thelike.

The method has the advantage of high current efliciency. The rate ofcleaning is easy to regulate within wide limits through simple currentmanipulations. It has the additional advantage pointed out hereinbeforethat as soon as the plating is substantially removed, the current flowstops since plutonium is rendered passive and is not soluble in theelectrolyte.

Because of the many possible variations it is to be understood that theinvention is not to be limited in spirit or scope except as indicated inthe appended claims.

What is claimed is:

1. The method of stripping metal coatings from plutonium metal bodies,said metal coating being selected from the class consisting of silver,nickel, cadmium, zinc and indium, which-comprises immersing theplutonium metal body as anode and a stainless steel body as cathode inan electrolyte essentially of an aqueous solution of trisodiumphosphate, and passing an electrical current at an anode current densityof from 0.1 to 1.0 ampere per square inch until the coatingmetal isremoved.

2. The method of stripping metal coatings from plutonium metal bodies,said metal coating being selected from the class consisting of silver,nickel, cadmium, zinc and indium, which comprises immersing theplutonium metal body as anode and a stainless steel body as cathode inan electrolyte essentially of an aqueous solution of trisodiumphosphate, and passing an electrical current at an anode current densityof 0.5 ampere per square inch until the coating metal is removed.

3. The method of stripping metal coatings from plutonium metal bodies,said metal coating being selected from the class consisting of silver,nickel, cadmium, zinc and indium, which comprises immersing theplutonium metal body as anode and a stainless steel body as cathode inan electrolyte consisting essentially of 100 grams per liter oftrisodium phosphate in an aqueous solution, and passing an electricalcurrent at an anode current f 2,907,700 7' y '7 H density of 0,5 ampereper square inch ilntil the coat- I ing metal is removed.-

2,436,244 Brenner et a1. Feb. 17, 1948 2,596,307 Stufier May113, .1952

4 OTHER REFERENCES Hoyt: Metal and Alloys, data book, page 285, ReinholdPubl. Co. (1943). e

Black: Metal Finishing, pp: 457, 458, November 1945.

Seaborg: Chem. Eng. News, vol. 23, page 2192 (1945).

The Actinide Elements, edited by Glenn T. Seaborg and Joseph J. Katz,1st ed. (1954), McGraw-Hill Book Co., N.Y., pages 373, 374.

1. THE METHOD OF STRIPPING METAL COATING FROM PLUTONIUM METAL BODIES,SAID METAL COATING BEING SELECTED FROM THE CLASS CONSISTING OF SILVER,NICKEL, CADMIUM, ZINC AND INDIUM, WHICH COMPRISES IMMERSING THEPLUTONIUM METAL BODY AS ANODE AND A STAINLESS STEEL BODY AS CATHODE INAN ELECTROLYTE ESSENTIALLY OF AN AQUEOUS SOLUTION OF TRISODIUMPHOSPHATE, AND PASSING AN ELECTRIAL CURRENT AT AN ANODE CURRENT DENSITYOF FROM 0.1 TO 1.0 AMPERE PER SQUARE INCH UNTIL THE COATING METAL ISREMOVED.